I'm on a contract in my current role....

Which seems to only be renewed every few months, I have been applying for other roles & mentioned it to my manager.... but i always get renewed at the last min... been there long enough & I finally got an interview but didn't tell my manager I applied.... should I now tell her I have accepted the interview or wait till I hear back from the interview if its a yes or no before saying anything to her?

FYI we are seriously understaffed & my manager didn't do anything & now all the pressure is on me... part of reason why I wanna leave...